Correlation between atomic rearrangement in defective fullerenes and migration behavior of encaged metal ions

Migration behavior of Gd³⁺ and Ca²⁺ ions inside C₈₂ fullerene cages with irradiation-induced atomic defects is observed using in situ high-resolution electron microscopy. The encapsulated Gd³⁺ ion can easily leave the fullerene cage through the defect, whereas the Ca²⁺ ion remains inside the defective cage. Density functional theory calculations prove that this atomic behavior closely correlates with the rearrangement of carbon atoms in defective fullerene cages. The Gd³⁺ ion disturbs the self-restoration of the defective cage and assists its polymerization, but such effects are not found for the Ca²⁺ ion.